1. Field of the Invention
The present invention relates to a multi-layer wiring circuit board and a method for producing the same, and particularly to a multi-layer wiring circuit board having thick layer portions and thin layer portions and a method for producing the same.
2. Related Art
Heretofore, a rigid flexible wiring circuit board has been used widely in a portable electronic appliance or the like because reduction in size and weight of the rigid flexible wiring circuit board and increase in density thereof can be attained. As shown in FIG. 3B, the rigid flexible wiring circuit board has a rigid wiring circuit portions 1, and a flexible wiring circuit portion 2. Electronic parts can be mounted on each rigid wiring circuit portion 1 to thereby carry out high-density wiring in the rigid wiring circuit portion 1. The flexible wiring circuit portion 2 is flexible so as to be foldable and is formed as a signal transmission path.
Such a rigid flexible wiring circuit board can be produced as follows. That is, as shown in FIG. 3A, a double-sided substrate in which first and second conductive layers 4 and 5 are laminated on opposite surfaces of a first insulating layer 3 is prepared so that second and third insulating layers 6 and 7 are laminated on the first and second conductive layers 4 and 5 of the double-sided substrate through first and second adhesive layers 15 and 16 respectively. Thus, a first board 8 is formed.
Then, a two-layered substrate in which a third conductive layer 10 is laminated on a fourth insulating layer 9 is prepared separately so that a cover insulating layer 11 for covering the third conductive layer 10 of the two-layered substrate is laminated on the third conductive layer 10 through a third adhesive layer 12. In such a manner, a plurality of second boards 13 are formed.
Further, as shown in FIG. 3B, the fourth insulating layers 9 of the respective second boards 13 are laminated on portions forming the rigid wiring circuit portions 1 in the second and third insulating layers 6 and 7 of the first board 8 through fourth adhesive layers 14 respectively. Thus, a rigid flexible wiring circuit is obtained.
In recent years, portable information communication apparatus such as cellular phone has been evolved into multi-function mobile apparatus having a camera function or the like as well as a related art telephone function. Accordingly, the demand for reduction in size and weight of a multi-layer wiring circuit board has been intensified. Also in the rigid flexible wiring circuit board, a rigid wiring circuit portion thereof is required to have a smaller thickness.